While commentators and political professionals are re-running the 1988 campaign (soft liberal Democrat gets shellacked by tough Republican) and the 1992 campaign (weak economy dooms Republican), let’s break from the pack and instead look at what the 1968 election might teach us about the 2008 contest.

Let’s agree from the start that most comparisons like this are specious. The year 1968 has almost no relation to 2008. Forty years ago there was no Internet, there were only three television networks (and people you knew actually watched the network news), there was a draft and there was Richard M. Nixon.

Here’s the political landscape four decades ago, vividly memorable for a large share of the baby boom generation, born between 1946 and 1964 and comprising the biggest population bulge in the nation:

Lyndon B. Johnson was a deeply unpopular president prosecuting a deeply unpopular war whose origins are wreathed in mystery, perhaps even in mendacity. We will for the moment skip the Democratic primary struggle, with its distracting but devastating climax (the death of Robert F. Kennedy in Los Angeles). For our purposes it is enough to recall that the Democrats nominated Vice President Hubert H. Humphrey of Minnesota, who was tied to Johnson and his unpopular war.

Humphrey would be worthy of a fulsome Wikipedia entry by virtue of his civil-rights speech at the 1948 Democratic National Convention alone. Yet his presidential campaign was doomed by his association with Vietnam and with Johnson. The best thing that Johnson did for him was to stop doing what he was doing (bombing North Vietnam), and that came only five days before the election – maybe not too little to help Humphrey but surely too late.

All of this comes to mind as Sen. John S. McCain of Arizona, the presumptive GOP nominee, struggles to define his relationship to George W. Bush. Theirs, like most political relationships, is complicated.

They both followed their fathers and grandfathers to the family college, McCain to Annapolis, Bush to Yale. They both enrolled in the family business, McCain in the Navy, Bush in oil and politics. McCain’s father and Bush’s father were both World War II heroes.

They both have spent their adult lives living down the colorful exploits of their youthful years, which in both cases can be summarized neatly in three words: wild and crazy. McCain and Bush are both outspoken, living by an ethos that also can be summarized in three words: ready, shoot, aim.

And yet McCain went to war during the Vietnam years, Bush did not (he was in the Texas Air National Guard). McCain spent the Vietnam years as a Navy pilot, Bush was a pugilist against political correctness at Yale (which, to be fair, required a courage all its own in the Class of 1968 – there’s that year again).

McCain’s worldview was shaped by his five years in a Hanoi prison; Bush’s worldview was shaped by his two years at Harvard Business School. McCain is skeptical about the hold business has over the political process; Bush is not. McCain is a maverick; Bush is not.

One of the most interesting differences between them: In the 2000 campaign, Mr. McCain was willing to explore expanding the military’s portfolio to include humanitarian efforts. Bush had little interest in “nation-building.”

These men, so similar and yet so different, collided in the year 2000, when McCain crushed Bush’s hopes for an easy path to the GOP nomination by defeating the Texas governor by 19 percentage points in the New Hampshire primary. Bush responded by beating McCain by 11 percentage points in South Carolina. The McCain family has neither forgotten nor forgiven the rancid rumors and tough-guy politicking undertaken by some of Bush’s supporters – including a smear involving the McCains’ daughter, Bridget, adopted from Mother Teresa’s orphanage in Bangladesh.

McCain is running to extend Republican control of the White House to 12 years, maybe 16. He is as closely identified with the Iraq war as Bush is. The two are closer than before, but anyone who watches the body language senses the formality rather than the familiarity in the relationship.

Lately, of course, it has been hard even to observe that. Some 83 days passed between the two most recent Bush-McCain meetings. The last one, on the tarmac of the Phoenix Sky Harbor International Airport, provided only 26 seconds’ worth of television footage. This is not TR and Will a century ago – not that the relationship between Theodore Roosevelt and William Howard Taft that elected the Ohioan to the White House in 1908 ended so terrifically.

If McCain wants to distance himself from Bush, his effort won’t seem nearly as awkward as Humphrey’s attempt to do the same thing from the president he served 40 years ago. Bush and McCain are known antagonists. Saying they have separate outlooks and separate views – and wildly divergent memories from 2000, an important crucible for them both – requires no stretch of rhetoric, or of reality. How McCain does it, however, is one of the great mysteries of the 2008 campaign, and one of the biggest challenges any presidential candidate has faced for years.